To the best of my knowledge, stumbling (defined by pure discovery and no access) has never been tested in court and as such there is no precident.
We are in virgin legal territory here, so be careful. Keep in mind though that 802.11b was designed to automatically associate with AP's, does that mean that the Orinoco client manager can land you in the clink? I kind of doubt it. knowingly trespassing though if a defiante no-no
BUT....
From experience, the (at least Canadian) authorties probably don't care since I had a CSIS employee as part of my Wardriving team in Vegas
If they do it, then so can I
Just my $0.02
Render